Some actors win audience attention effortlessly; most have to work for it. Allison Pistorius is in the former group. When she comes on stage, you want to watch her. When she leaves, you feel a moment's regret. This quality stood her in good stead in the role of the jilted Helena in A Midsummer Night's Dream, a part that's too often cartoony or forgettable. In this Denver Center Theatre Company production, Pistorius got in a bunch of lively slapstick: furious struggles with her perceived rival, Hermia, enraged encounters with the two men who alternately pursued and rejected her, a memorable soaking. But despite all this, she made the character warmly human.